This invention relates to welts on unit shoe soles.
Traditionally, shoe uppers have been stitched to leather soles so as to leave a decorative welt around the periphery of the sole. Today, with the advent of unit soles, uppers are attached to the sole by cement; to preserve the traditional appearance, a separate welt is attached to the unit sole around the periphery of the upper.
Such unit sole welts are typically vinyl strips, often having stitching running the length of the welt, with the bobbin thread running along a stitching groove on the underside of the welt. This stitching groove gives the welt a generally U-shaped cross-section.
A flange is often added to the welt to improve the bond between the welt and unit sole. The welt flange is cemented between the upper and sole. Because such a flange reduces the cement bond area between upper and sole, it is often pinked to reduce its surface area.